A device for protecting a passenger in a vehicle includes an airbag system disclosed in, for example, US 2004/0164534 (JP 2004255911A). This airbag system includes a safety switching element (safety switching element purpose), a high-side (high-potential side) switching element and a low-side (low-potential side) switching element formed in an integrated circuit (IC). The safety switching element, high-side switching element and low-side switching element are connected in series. The safety switching element is connected to a power source. Further, a squib is interposed between the high-side switching element and the low-side switching element.
When all the switching elements are driven to turn on, an electric current flows into the squib to ignite it. Accordingly, the airbag deploys to protect a passenger in the vehicle.
Usually, however, the high-side switching element connected on the high-side of the squib is so driven that a predetermined current flows into the squib. An overshoot current flows if the high-side switching element is driven earlier than the safety switching element or the low-side switching element. For example, when an electric current is fed to a plurality of squibs through the safety switching element, overshoot currents generated in the squibs are overlapped one upon the other and flow into the safety switching element. Therefore, it becomes necessary to use the safety switching element having a large rated current making it difficult to suppress the cost of the airbag system.